1. Field of the Invention
The present invention relates to compounds and a process for producing the compounds.
2. Description of the Related Art
In order to detect lesion markers present at lesion sites, imaging contrast agents for in vivo diagnosis have been developed. Some of the imaging contrast agents are compounds having lesion marker binding molecules such as antibodies labeled with physical signal generating molecules. As the signal generating molecules, such as radioactive nuclides, molecules which emit magnetic resonance imaging (MRI) signals, molecules which emit supersonic wave signals and molecules which emit fluorescence signals have been known. To detect lesion sites and lesion markers, such an imaging contrast agent is administered to a living body and the signal from the signal generating molecule within the agent is detected from outside the body.
However, when such a compound as above is administered to the blood, the compound may bind to lesion markers present at sites other than lesion sites, for example, lesion markers escaping from the lesion sites and present in the blood and lesion markers present at normal sites and consequently the amount of the compound which reaches the lesion sites may decrease. Also, in such a case, high contrast detection of the lesion sites is difficult because the compound bound to sites other than the lesion sites and detected as background signal.
To solve the problem mentioned above, Lauffer et al. reported prodrug imaging contrast agents which were made biologically active in vivo in the presence of specific biological activity (Japanese Patent Application Laid-Open No. 2000-507577). The prodrug imaging contrast agents disclosed in this document are those in which a target molecule having a signal generating molecule is bound with a molecule which reduces the binding ability of the target molecule through an enzyme-cleavable linker. The linker is cleaved in a reaction with an alkali phosphatase and, as a result, the binding ability of a low molecular weight compound used as a target molecule with human serum albumin increases as compared with that prior to the cleavage. Lauffer et al. also reported that the cleavage of the linker changed the signal of the MRI signal generating molecule and the detection of the lesion sites were enabled with higher contrast.
Antibodies are molecules which specifically recognize antigens. Antibodies are preferably used for the detection of lesion sites or treatment. Japanese Patent Application Laid-Open No. 2000-507577 describes the possibility of using a low molecular weight compound as a imaging contrast agent but does not disclose the molecular design and the preparation method of the imaging contrast agent, and thus the utility of the imaging contrast agent using an antibody which is made biologically active in vivo has not been known.